DE-OS No. 27 40 573 discloses a locking device for the tail board or sides of trucks, which is provided with a swivel bolt, which is mounted in a housing by means of a pin. Within the housing is formed a force transfer zone, on which engages a two-armed angular pressure piece, which is also mounted by means of a pin. A manual rocking lever is articulated to one arm of the angular pressure piece. If a swinging pin passes in to the vicinity of the open swivel bolt, then by means of the manual rocking lever an operator deflects the angular pressure piece outwards acting on the compressive force transfer zone of the rocking lever. In order to reduce the frictional forces which occur, a roller with a pin is mounted in this zone on the rocking lever. As a result of the force transfer, the swinging pin is forced into the jaw. On opening the angular pressure piece engages on a cam extension on the swivel bolt, which is moved outwards. To ensure that the tail board pin is held in rattle-proof manner in the closed position, the swivel bolt is at least partly made from an elastic material. In addition, a slot is provided in which are located two disk springs, which press the elastic bolt zone onto the swivel pin.
This locking device suffers from the disadvantage that all the closing a retaining forces acting on the swivel bolt have to be absorbed by the swivel bolt trunnion and the angular pressure piece trunnion. If one of these trunnions or a pivot bearing does not withstand this pressure, the trunnion jumps out of the jaw. There is also a risk of the swivel bolt breaking in the case of an excessive pressure of the trunnion, especially as it is slotted. With regards to the roller, it is to be expected that when transporting highly corrosive products, e.g. artificial fertilizers, residues will collect in the interior of the housing and the roller will become blocked through rust.
DE-OS No. 29 32 763 discloses a locking means for hinge down and swing out tail boards of trucks, in which a locking rocker fulfills the function of bringing the swinging pin into the jaw and maintaining it therein. The manually operable locking rocker is articulated pivotably to a jaw part by means of two connecting rods. The locking rocker is held in the closed state by a safety catch. It is a disadvantage of this locking device that all forces have to be absorbed by the swivel bearing bolt, so that there is a risk of breakage in the case of higher forces.
DE-OS No. 29 36 528 discloses a long-path locking means for hinge down and swing out tail boards, which is operable by means of a handle with a dead centre means. Upstream of a jaw is located a pivotable locking rocker, which is mounted by means of a bolt in the side walls of housing. In a further bolt, a toggle lever is articulated to the locking rocker and is connected by means of a knuckle joint to a second toggle lever also mounted in the housing wall with a bolt. This lever mechanism, which assumes a beyond dead centre position when the locking rocker is closed, is moved by means of a push rod suspended on the knuckle joint and leading to the handle, a lever action being exerted on the locking rocker by means of the toggle levers. It is a disadvantage of this locking device, that the reliability and operation are exclusively dependent on the bolts and if a single bolt fails it can no longer fulfill its function. In addition, all joints are naturally subject to wear, so that at least in the case of frequent operation and vehicle and swinging pin impacts the ball and socket joints can become deflected. This disadvantage cannot be compensated by the tensioning or clamping function of the beyond dead centre system, because such systems perform a setting movement. It is not possible to readjust the clearance of the articulated points, so that rattling occurs during all vehicle movements following a certain amount of wear, whereby such rattling must be avoided so as not to make the work place unduly noisy.
Finally, DE-OS No. 29 40 671 discloses a locking device for walls, doors, flaps and reciprocally pivotable plates, in which the trunnion pin is held in the jaw by a displaceable bolt. The end of the bolt is constructed as a gripper for engaging in a corresponding recess on the trunnion pin. As soon as the bolt grips the trunnion pin, there is a centering and guidance in the jaw. The bolt is guided in a stable housing, which absorbs in large-area manner the forces from the swinging pin. This locking device admittedly functions reliably, but for trapping the swinging pin it has to be introduced a relatively long way into the jaw opening.